This invention relates to an adjustable steering column for a vehicle, and more particularly to the type of column which can be adjusted, within a limited range, between an infinite number of degrees of telescoping or longitudinal extension and preferably also between several positions of vertical tilt.
It is known to provide tilting and telescoping steering columns for industrial and agricultural vehicles, as well as for automobiles. Generally, these have been provided for the convenience of the operator. The ability to adjust a steering wheel to various positions of extension or of both tilt and extension contributes to convenience by allowing operators to adjust for most comfortable steering and for easiest entrance and egress. Different operators may, and often do, prefer different adjustments, or the same operator may prefer different adjustments for different working conditions; for example, he or she may prefer to stand while operating a tractor or other vehicle for one purpose, and to sit while operating it for another purpose.
Unfortunately, the adjustability intended to be provided by telescoping steering columns of known design suitable for industrial and agricultural vehicles has often been, in important respects, more theoretical than practical. In particular, adjustment between different degrees of telescoping or longitudinal extension has often been difficult for the operator to accomplish. Indeed, such adjustment may be impossible to accomplish without pounding the column with a hammer, heavy wrench, or other implement, to thereby apply brute force to "break" the column away from a locked condition at its then-set degree of telescoping so that it can be shifted and set at another degree of telescoping. At the new setting, the column may again establish a locked condition which will again have to be "broken" by brute force upon subsequent adjustment. Under such circumstances, adjustment may not be worth the bother, particularly where true convenience would require frequent adjustment back and forth between positions.
Examples of prior art columns include Treichel et al. U.S. Pat. No. 3,791,223 and Hansen U.S. Pat. No. 4,257,624. Each of these patents illustrates a telescoping steering column whose length is adjustable over a continuous range between upper and lower limits of full extension and full retraction. In each of these patents, cam surfaces, a wedge nut (82 or 32), and a cooperating shaft member interact to wedge the nut and shaft member against an outer shaft member and lock the linkage in any selected degree of telescoping adjustment. However, such lock may be difficult to "break". It is intended that backing off or rotation of a lock-unlock knob (74 or 40) in the unlocking direction will release the linkage from the locked condition, but when a tight lock exists, the intended result may not occur. Instead, the control rod (72 or 37) may shift axially in such a way as to allow relative movement between the threadedly engaged nut and control rod without releasing the locked condition. The "brute force" approach of pounding or hammering may then be required to break the linkage from its locked condition.
More recently, steering columns have been provided which minimize or totally eliminate the problem of breaking away from locked condition. In such improved columns, means is provided for constraining a threaded control rod member against certain relative axial movement while it is being rotated in the direction intended to release the column from locked condition. Such constraint is imposed in such a way that axial movement of a wedge nut engaged with the rod is positively forced, thereby forcing a breakaway from the locked condition. The result is a telescoping steering column whose length can be adjusted over a continuous range of column lengths and with much greater convenience than before. Examples are shown in U.S. application Ser. No. 369,495 filed Apr. 19, 1982, of common assignee.
However even in such improved columns, problems remain in respect of convenience of use because of the uncertain and excessive amount of rotation required to lock the column in adjusted position or to force the breakaway from locked condition. While both locking and breakaway will eventually occur in a positive manner, the action of the linkage tends to feel mushy and uncertain to the user because of the excessive rotation required to complete the action. The time and effort required to complete higher degrees of rotation also detract from convenience of use.